Isomerization of paraffin hydrocarbons with molybdenum oxide-alumina catalyst



A ril 17, 1956 CLARK ET AL A. ISOMERIZATION OF PARAFFIN HYDROCARBONS WITH MOLYBDENUM OXIDE-ALUMINA CATALYST Fil-ed Jan. 21, 1952 TE MP. F 860 90 PREss- PSIG 50o sP. VELOCITY fi/ I. 3 FEED-me ULTIMATE YIELD OF 150 PENTANE PLUS OTHER LIQUID PRODUCTS 70 I 6O I O 5o B TOTAL CONVERSION OF N-PENTAN E PER PASS 4o H2 /c MOL o I 2 4 J INVENTOIS A 7' TOR/YEVS United States Patent ISONIERIZATION 0F PARAFFIN HYDROCARBONS WITH MOLYBDENUM OXIDE-ALUMINA CAT- ALYST Application January 21, 1952, Serial No. 267,408

15 Claims. (Cl. 260-6835) This invention relates to an improved process for the isomerization of parafiin hydrocarbons. In one of its more specific aspects this invention relates to a process for the isomerization of normal pentane, normal hexane and normal heptane hydrocarbons. In another of its more specific aspects the invention relates to an improved isomerization process in which molybdenum oxide silicaalumina catalyst is contacted with parafiin hydrocarbons in the presence of predetermined amounts of hydrogen.

Paraflin isomerization has been practical with the use of a number of catalysts, among which, one of the most commonly used is aluminum chloride. The isomerization of parafiins is highly desirable when the hydrocarbon is to be used as a motor fuel, for by this means the low octane normal parafiins are converted to isoparaflins of substantially higher octane number. Normal butane has been very successfully isomerized in the presence of aluminum chloride. However, the higher paraflins, for example normal pentene, normal hexane, and normal heptane are not so well suited for isomerization by this process, for these hydrocarbons crack quite readily to give degradation products rather than isomers of the feed material. Thus, the ultimate yield obtained by this isomerization process is relatively low.

Furthermore, the isomerization of these paraflins over other catalysts, indicated by the prior art, has been conducted at'the expense of either the per pass conversion or the ultimate yield obtained.

In at least one embodiment of this invention at least one of the following objects is attained.

It is an object of this invention to provide an improved process for the catalytic isomerization of parafin hydrocarbons. Another object is to provide a process for the isomerization of paraflin hydrocarbons wherein a high yield of product can be maintained when the rate of feed to the process is high. Another object is toprovide an improved isomerization process wherein carbon deposition or formation upon the isomerization catalyst is reduced. Another object is to provide an improved process for the isomerization of normal pentane, normal hexane and normal heptane in the presence of a catalyst comprising alumina and molybdenum oxide. A further object is to provide an improved isomerization process wherein the ultimate yield of isomerizateand the per pass conversion of normal parafiin hydrocarbon are maintained at high levels when a high feed rate of normal paraflin hydrocarbon is employed. It is still another object to provide a method for controlling the temperature of the exothermic isomerization reaction.

-We have discovered that by conducting the isomerization of pentane, hexane, or heptane or admixtures thereof over a catalyst comprising molybdenum oxide and alumina, under carefully controlled isomerizing conditions and in the presence of a carefully controlled. amount of hydrogen, preferably in the range 0.3 to 0.8 mol of hydrogen per mol of hydrocarbon feed, that high feed rates 2,742,519 Patented Apr. 17, 1956 unexpected high ultimate yield of branched-chain isomers of the feed hydrocarbons. We have further discovered that the temperature of the exothermic isomerization reaction can be controlled by admixing predetermined amounts of cyclic hydrocarbons with the feed to the process.

It is known that cyclic hydrocarbons act as catalyst poisons in an isomerization reaction conducted in the presence of a molybdenum oxide-alumina catalyst if such in admixture.

cyclic hydrocarbons are present in amounts greater than about 5 volume per cent of the normal paraflin hydrocarbons being processed. We have found that amounts of cyclic hydrocarbons in the range of about 0.5 to 5 volume per cent and preferably in the range 1 to 3.0 volume per cent of the normal paraflin hydrocarbon feed can be tolerated by the catalyst. In the process of this invention the cyclic hydrocarbons are dehydrogenated and the dehydrogenation reaction is strongly endothermic. The deleterious effects, if any, of the small quantities of cyclic hydrocarbons used in the practice of this invention are more than oifset by the close temperature control, of the exothermic isomerization reaction, thus provided. The cyclic hydrocarbons can be introduced to the isomerization zone by blending a controlled amount of commercial hexane with the normal pentane, normal hexane or normal heptane feed stream. The cyclic hydrocarbon content of commercial normal hexane is approximately 20 to 25 per cent, the principal cyclic being methyl cyclopentane. Cyclic hydrocarbons from other sources can be used. I

Normal pentane, normal hexane and normal heptane can be isomerized separately or in admixture by the practice of our invention. A preferred method is to employ a separation step wherein heptane is removed and isomerized separately and pentane and hexane are isomerized This is particularly true When the commercial grade of hydrocarbons are isomerized. Commercial pentane is exothermic reacting whereas commercial hexane and commercial heptane are endothermic reacting. Thus commercial hexane and commercial pentane can be blended together or commercial pentane and commercial heptane can be blended together so as to control the temat temperatures in the range 790 to 880 F., pressures in are possible with unexpected high conversion rates and the range 450 to 700 pounds per square inch, mols of hydrogen per mol of hydrocarbon in the range 0.3/ 1.0 to 0.8/1.0 and liquid hourly space velocity in the range 0.6 to 2.0. i

I The following conditions are the preferred ranges for isomerization of the hydrocarbons listed:

Table Ill-C5 11-05 Il-O7 Temperature, F .i- 830-880 800-860 790-850 Pressure, p. s. i 450-700 450-700 450-700 M015 Hz/Mols HO 0.30:10.80:1 0.30:10.80:1 0.30:l-0.80:1 LHSV l. 1-1.6 0. 8-1. 4 0.8-1. 4 Oyclics, Vol. Percent... 0.5-3.0 0.5-3.0 0. 5-3. 0

amount of a cyclic hydrocarbon to control the temperature of the exothermic isomerization reaction.

In the practice of this invention there is obtained a high conversion per pass with a high feed rate combined with the further features of this invention which are, a high ultimate yield of isomer, and improved temperature control.

The attached drawing is a graphical illustration of the high ultimate yield and high conversion that is obtained by the practice of this invention.

The following examples illustrate the high conversion per pass and high ultimate yield obtained by the practice of this invention.

EXAMPLE I This run shows conditions suitable for isomerization of normal pentane over a catalyst consisting of 7% weight per cent molybdenum trioxide, about 4 /2 weight per cent silica, and the remainder alumina. The molybdenum trioxide was reduced by means of hydrogen prior to use. This test run was made at a temperature 830 F., a pressure of 550 p. s. i., space velocity of 1.25, and a hydrogen-to-hydrocarbon ratio of 0.58. The hydrogen used was not pure, containing 87 volume per cent hydrogen. The conversion obtained under these conditions was 46.2 per cent, and the ultimate yield of isopentane obtained was 90.5 per cent.

EXAMPLE II In this example, one suitable set of conditions for the isomerization of normal hexane is shown. The catalyst used is the same catalyst as was used in the previous example and had been regenerated following that run. The temperature was 815 F; the pressure, 515 p. s. i.; space velocity, 1.0; and the hydrogcn-to-hydrocarbon ratio, 0.68. The hydrogen used in this run was pure hydrogen. The conversion obtained under these conditions was 51.7 percent and an ultimate yield of isohexanes of 88.4 per cent was obtained. The C5+ material was obtained in an ultimate yield of 92.2 weight per cent.

EXAMPLE III A series of runs were made employing a catalyst whose composition was 6.4 weight per cent molybdenum oxide, 4.6 weight per cent silica and 89.0 weight per cent alumina, in the isomerization of normal pentane under comparable operating conditions. The results of these runs are tabulated in Table I and are shown graphically in the drawing.

Table I Space Total Hi/PGH' Ult. Run No. tane M01 a 5 5,31 2%; Yield S?- f f Ratio 1 Per'cent' of 105 2. a so. 67. s 800 51s 0. 0s 2. 1 23. s 74. 7 860 515 0. 32 1. a 55. 6 s2. 5 850 515 o. 515 1. a 52. 5 so. a 860 515 o. s 1. a4 49. 6 8?. a sec 515 0. 9s 1. 25 52. s 63. s 860 515 1. 45 1. 29 53. 5 5a. 2 860 515 a. 28 1. 2s 40. 1 62. s 860 515 s. s 1. 32 53.1 69.0 860 515 7. a 1. 2s 31 7 60.0 860 515 Catalysts containing from 5 to 30 weight per cent molybdenum oxide and the remainder being alumina with no silica present can be employed in the process of this invention with satisfactory results. The presence of silica in the catalyst exerts a stabilizing effect upon the catalyst during runs extending over long periods of time. Thus the presence of silica is not believed necessary for the immediate activity of the catalyst but is desirable for continued operation.

Variation and modification are possible within the scope of the foregoing disclosure and the appended claims to the invention the essence of which is that high ultimate yield of isomers and high. rates of conversion per pass at high feed rates can be obtained in the isomerization of pentane, hexane and heptane when the said paraffins are contacted with a catalyst comprising molybdenum oxide and alumina within the certainnarrow limits of isomerizing conditions disclosed herein, particularly the ratio of hydrogen to paraffin hydrocarbon feed and further that the temperature rise of the exothermic isomerization reaction can be controlled by the addition of a minor amount of cyclic hydrocarbon to the parafiin hydrocarbon feed.

We claim:

1. A process for the isomerization of normal paraffin hydrocarbons having from 5 to 7 carbon atoms per molecule which comprises contacting said hydrocarbons with a catalyst comprising molybdenum oxide and alumina at temperatures in the range 790 to 880 F., pressures in the range 450 to 700 pounds per square inch, mols of hydrogen per mol of hydrocarbon feed in the range 0.3/1.0 to 0.8/1.0, the liquid hourly space velocity in the range 0.8 to 1.6 and volumes of a cyclic aliphatic hydrocarbon per volume of paraffin hydrocarbon feed in the range 0.01/10 to 0.05/10.

2. The process of claim 1 wherein the catalyst comprises molybdenum trioxides in the range 5 to 30 weight per cent, silica in the range 0 to 10 weight per cent, the remainder being alumina and the said catalyst is reduced in hydrogen prior to use in the said isomcrization reaction.

3. The process of claim 1 wherein the paraffin hydrocarbon is pentane.

4. The process of claim 1 wherein the paraflin hydrocarbon is hexane.

5. The process of claim 1 wherein the parafiin hydrocarbon is heptane.

6. In a process for the isomerization of normal paraffin hydrocarbons having from 5 to 7 carbon atoms per molecule in the presence of a catalyst comprising molybdenum oxide and alumina the improvement which comprises maintaining the mol ratio of hydrogen to paraflin hydrocarbon feed in the range 0.3/1.0 to 0.8/1.0.

7. In a process for the isomerization of normal paraffin hydrocarbons having from 5 to 7 carbon atoms per molecule in the presence of a catalyst comprising molybdenum oxide and alumina the improvement which comprises in combination; maintaining the mol ratio of hydrogen to paraflin hydrocarbon feed in the range 0.3/1.0 to 0.8/ 1.0 and admixing with said paraflin hydrocarbon a cyclic aliphatic hydrocarbon in the range 1 to 5 volume per cent of said parafiin hydrocarbon.

8. A process for the isomerization of normal paraflin hydrocarbons having from 5 to 7 carbon atoms per molecule which comprises contacting said hydrocarbons with a catalyst comprising molybdenum oxide and alumina at temperatures in the range of 790 to 880 F., pressures in the range 450 to 700 pounds per square inch, mols of hydrogen per mol of hydrocarbon feed in the range 0.3/ 1.0 to 0.8/1.0, and the liquid hourly space velocity in the range 0.8 to 1.6.

9. The process of claim 8 wherein the paraffin hydrocarbon is pentane.

10. The process of claim 8 wherein the parafiin hydrocarbon is hexane.

11. The process of claim 8 wherein the paraffin hydrocarbon is heptane.

12. The process of claim 8 wherein the paraffin hydrocarbon is a mixture of pentane and hexane.

13. The process of claim 8 wherein the normal parafiin hydrocarbon is normal pentane; the catalyst comprises 5 to 30 weight per cent molybdenum oxide, 0 to 10 weight per cent silica and the remainder alumina; and the isomerizing condition-s comprise a temperature in the range 830 to 880 F., pressure in the range 450 to 700 pounds per square inch, a space velocity in the range 1.1 to 1.6 and a hydrogen to hydrocarbon ratio in the range 0.3/1.0 to 0.8/1.0.

14. The process of claim 8 wherein the normal parafiin hydrocarbon is normal hexane; the catalyst comprises 5 to 30 weight per cent molybdenum oxide, 0 to 10 weight v per cent silica and the remainder alumina; and the isomerizing conditions comprise a temperature in the range800 to 860 F., pressure in the range 450 to 700 pounds per square inch, a space velocity in the range 0.8 to 1.4

and a hydrogen to hydrocarbon ratio in the range 0.3/1 to 0.8/ 1.

15. The process of claim 8 wherein the normal parafiin" is heptane; the catalyst comprises 5 to 30 weight per cent molybdenum oxide, 0 to 10 weight per cent silica and the remainderalumina; and the isomerizing conditions com References Cited in the fileof this patent Turkevich et al.: Jourt Amer. Chem. Soc., vol. 68,

UNITED STATES PATENTS Groll et a1 Dec. 19, 1939 Greensfelder Jan. 15, 1946 Howes et a1 May 7, 1946 Keith Feb. 18, 1947 Smith July 29, 1947 OTHER REFERENCES pages 519-520, February 1941 (2 pages). 

1. A PROCESS FOR THE ISOMERIZATION OF NORMAL PARAFFIN HYDROCARBONS HAVING FROM 5 TO 7 CARBON ATOMS PER MOLECULE WHICH COMPRISES CONTACTING SAID HYDROCARBONS WITH A CATALYST COMPRISING MOLYBDENUM OXIDE AND ALUMINA AT TEMPERATURES IN THE RANGE 790 TO 880* F., PRESSURE IN THE RANGE 450 TO 700 POUNDS PER SQUARE INCH, MOLS OF HYDROGEN PER MOL OF HYDROCARBON FEED IN THE RANGE 0.3/1.0 TO 0.8/1.0, THE LIQUID HOURLY SPACE VELOCITY IN THE RANGE 0.8 TO 1.6 AND VOLUMES OF A CYCLIC ALIPHATIC HYDROCARBON PER VOLUME OF PARAFFIN HYDROCARBON FEED IN THE RANGE 0.01/1.0 TO 0.05/1.0. 